Teletypewriter switching system



April 2x1, 1942. F. SKINKE'@ Em- '2,280,292

` TELETYPEWRITER' SWITCHING SYSTEM v 8 sheets-sheet 2 Filed July l1'?, 1940 A T TOR/VE y n y l o, k E u,

' April 21 1942. F. s. KINKEAD ETAL y 2,280,292

TELETYPEWRITER swIToHNG SYSTEM 'Fil-ed July` 17, 1940 e sheets-sheet s REPEA TER Nol/o ATTORNEY April 21, 1942. F. s. KINKEAD -ET AL TLETYPEWRITER SWITCHING SYSTEMl Filed July 17, 1940 8 sheets-sheet 4 8 Shcleets-Shet 5 Filed July 17, 1940 F. S. KINKEAD ErAL TELETYPEWRITER swITcHING SYSTEM N m w w w mm. WQ, www# wwm L h g. .V f V my HH Hu HH 1H r N nun nui nn n nun M m mwm mhm ST @hm Ra w Vn-.-mmu HHI F HHH AH HH HHM, y Ef ,w m- Wm 3mm gf ,V-. f lw April 2.1, 1942.

April 21, 1942.'-

-{F. sz KINKEAD Erm. 2,280,292. TELETYPEWRITER swIT-CHING SYSTEM Filed July. 17, 1940 '8 sheets-sheet e u ..0 y .n.nn nu." .nnI .my W I. m A ma .m uw. @mm mw my w A Md. WJ lll lll lll T ...N ...nu nun nun S\\ Mc Q E.. A ,E .u u uw w www if .nun M nun w Inn Hu "nu HUN nF; l .EA l l, EL wr. fm ww E y y ...mg 1 3% ,IW nl. kbWOUm Q n April 21; 1942.

' F. s. KIYNKEAD ETAL TELETY'PEWR'ITER SWITCHING SYSTEM a Sheets-sheet 84 V Filed July 17, 1940 @Ruy kkk

.Sul

, gls

L N nog By A frREcE/p l Q7/M Patented Apr. 21, 1942l E Fullerton S., Kinkead; New York, andl Joseph A. Krccck, New Rochelle, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New` York,.N. Y'.,a corporation of'New York `Application July 17, 1940,` Serial No.` 34:5;398 a claims. (ci. ris- 2) Thisrelates to printing telegraph systems and* more particularly to switching arrangementsadapted to give service to stations connected to a main station in an intercommunicating teletypewriter system.

The system is particularly useful in banks, and manufacturing concerns as well as pressA associations and police departments wherein it is highly desirable to provide broadcast and conference facilities for not only the main station but also for each of the local andthe outlying stations.

An object of the invention isto meet a widel variation in intercommunicating system requirements with a minimum effect on the cost.

Another object istoprovvde a closed "line circuit which `will indicate incoming calls, provide proper supervision and facilitate broadcasting control.

Another object is to provide anarrangement whereby lines may be connectedto a. common, circuit for hub transmission.`

According `to the present invention, a teletypewriter intercommunicating system is `provided wherein amanually operated switchboard at a switching center is used` for terminating a` plurality of local loops from near-by stations and extension lines from outlying stations.`

Each of the loops and lines is in series connection with a repeater at an intermediate location and a line control circuit at the switching center. Each of the control circuits is connected` to a row of keys whereby each line may be extended through any one of six hub circuits;` to

either of two operators teletypewriter sets. Two" rows of keys are provided for respectively con,-n

necting two, operators teletypewriter sets to the hub. circuits, one key of each row being in en-4 gageable relation with each hub circuit. The key arrangement for interconnecting lines may be replaced by a cord connecting system, each cord of the system containing keys for connecting the operators set and for arranging the lines in broadcast groups as desired. There ispro'- vided vselective or general broadcast facilities for use by either operator or Astation attendant, or l subscriber, with individual acknowledgement from each line, selective or general conference facilities without individual .'.icli'nowledgerrient,`

and unattended station service.` The normalcapacity of the switchboard'is ten lines with a provision for a maximum of twenty-two lines. More than one switchboard with appropriate toll line facilities may be used in larger systems.

A feature of the invention1 is theprovision of 55` a normal arrangement wherein may be made iive 'simultaneous through-connections with a possibility of six if a path, or hub-circuit, is not reserved for broadcast.

Another feature is the broadcast facility whereby theswitchboard operator and the sta-` tion attendant are able to broadcast over a selective or general connection with individual acknowledgement from each station.

`Another feature is the establishment of al conference circuit over a selective or general connection without individual acknowledgement.

Another feature `is the closed loop with timed Y `spacedsignals for station calls and station dis-l connects.`

Another featureis the provision of unattended Y service which'permits starting and stopping the teletypewriter motor at a distant station from theswitchboard at the switching center.

Another feature is the optional provision of means whereby a .line' circuit may be automatically varranged for broadcast in such a manner" that interference with it from a subscriber using another line circuit will be impossible while an operator at the main station. switchboard is broadcasting to a group of subscribers.

Another feature is the provision of means for' establishing of interconnection of lines and connection between lines and operators teletypewriter sets by keys and inverse neutral circuits,

the latter circuits herein referred to -as hub circuits. Y GENERAL D'nscmrTIoN The `present system is adapted for either key 1 or cord circuit. switching. Each of the line cir-- cuits which terminate in the switchboardfincludes a loop repeater and a. supervisory con-- trol circuit. Two types of loop repeaters are provided, one for each ofthe local loops and the other for. each extension line. The extension lines are of considerable length andare referred toherein as the toll line extension circuits.' The line circuits operate on a closed' loop basisl andY therefore each station teletypewriter equipment: is furnishedwith meansA to start-on-closeaftert break and with "stop-signal-motor-control-ar-l rangement. The inverse neutral. method'of op'-v eration, also known as the hubA circuitlmethod;y is employed in the. basic switching circuitsiofl the system herein described. EachV of thev re1- peaters in the line circuits`V is arranged to.` be connected by means of the switching. keys-atfthe switchboard to' a hubso that the attendantsat stations connected to the line circuits maycommunicate with each other either individually or in broadcast or in conference arrangements. The sides of the repeaters connected to the subscribers stations are arranged to use a single polarity balanced, or differential, type of loop and the armatures of the repeating relays are arranged by means of the switching key to be connected to a common electrical point such as a hub circuit. In the idle condition equal impedances and voltages will be presented by all repeaters to a hub circuit through the windings of all the send relays to a potentiometer and no current will flow through the upper windings of the send relays. All these send relays will normally be held in a marking condition by current through their respective lower windings and all loops will therefore be closed. From the description which hereinafter follows, it will be seen that a relatively simple interconnecting arrangement is provided at the switchboard because from a transmission standpoint it is necessary to switch only one wire and for conference and broadcast circuits, additional stations maybe readily connected and disconnected from the hub circuit as desired without additional design complications.

Loop repeaters for local loops Stations located within the mileage resistance limitation for loop operation, say about 35 miles, are connected to the switchboard througha tworelay loop repeater. The relays of this type of repeater are known as the send and the receive relays. The side of the repeater connected to the switchboard is adapted for connection to a 13G-volt inverse neutral circuit, or hubA circuit, and the loop side of the repeater is a balanced, or differential, loop arrangement with positive 13G-volt battery when marking and ground for spacing. The bias winding of the receive relay is connected to a potentiometer which supplies a voltage to prevent the receive relay operating to spacing when a space signal is sent to the loop.

For Zoop extension circuits Stations served over loop extension circuits are connected to the switchboardthrough a three relay repeater. The repeater of this type comprises a send, a receive and a hold relay. The switchboard side of the repeater is adapted for connection to a positive 13D-volt inverse neutral, or hub circuit, and the other side is connected to an open-wire grounded telegraph line 'and is arranged to transmit signals of GO-milliampere current and no current. The hold relay is required, in vaddition to the sendand receive relays, to maintain a marking condition for the receive relay when signals are transmitted to the loop. i

Operators teletypean'z'ter circuit or position circuit and consists, from a transmission standpoint, of anv inverse neutral loop repeater with a send and a receive relay. The hub lead to the key switching circuit is connected to the armature of the send relay and the line winding of the receive relay. The receive relay is held on its marking contact in the idle condition due to current through its bias winding and no current ilows in the line winding since both sides are connected to taps on a positive 13G-volt battery (one tap being located at the marking contact of the send relay). Also, when idle, current flows through both windings of the send relay and the current flowing through the line Winding is a marking current of sulicient value to overpower the spacing effect of the bias winding.

Two separate and independent connections are made to the teletypewriter, one for the sending contacts and the other to the receiving or printer magnet. The send relay is responsive to signals from the sending contacts of the teletypewriter and when this relay is spacing, it applies ground to the hub circuit of an established connection and also to the line winding of the receive relay. The receive relay operates on signals sent from the teletypewriter and thereby provides local copy. The receive relay transmits signals to the teletypewriter, or printer, magnet on an open and close basis.

Conference connection By reference to the key switching circuit it will be seen that one or more station keys may be operated to the same level and a conference connection, that is, two-way communication between all interconnected stations will be established. In this case individual supervision on disconnect or acknowledgment will not be obtained because an open signal of uve-second duration sent by any station will be received by all control circuits and all supervisory lamps will light and the operator will not know who is sending the signal.

Broadcast connection Three forms of broadcast connections may be established. They are a selected and a general broadcast from the switchboard operator and a broadcast by any station to a group of stations selected by the operator.

Selected broadcast The operator operates the broadcast key in one of the operators set circuits to the selected position and an operators set key in the same set circuit to the level from which the broadcasting is to take place. Line keys for the desired stations are also operated to the same level as the operators key. A short break signal is sent by the operator and all stations start simultaneously.

General broadcast (seizure and non-seizure) A general broadcast to a portion or all the stations of a network may be arranged on a predetermined basis by the use of particular wiring connections associated with the broadcast relay in each of the control circuits. For a common or a general broadcast connection, the operator operates a broadcast key in one of the operators set circuits to the group position and if no stations other than those in the predetermined group are to receive the broadcast method, no line keys or operators keys are operated. Individual acknowledgment will be obtained as in the selected broadcast arrangement.

Station broadcast A station may broadcast to a group of stations selected by the operator by using two levels of switching keys, that is, two hubs in the switching circuit. These key operations establish a oneway circuit to all stations receiving the broadcast and the operator at the switchboard and the attendant at the station transmitting the broadcast, may communicate on a two-way basis. Individual acknowledgment of the broadessences cast` method will be obtained from all' stations arranged for one-way service.

Referring to the drawings:

Fig. 1 shows a diagrammatic arrangement ofpeater and well known inthe art, and in dia grammatic form, two other stations `and associatedrepeaters of types-respectively similar to thoseshown somewhat indetail.` The repeaters are ofthe two-way halfy duplex type and areparticularly adaptable for use in` local subscribers loops; t l

Fig. 3 shows, somewhat in detail, anothersubscribers local loop station. This local loop station, however, is connected iirst through al pair of terminal repeaters and thenthrough another type of repeater adapted for toll lines.` The lastmentioned repeater is used in lines arranged to furnish service to subscribers at distant` outlying points;

Fig, 4 shows, in detail, at a main switching office, a closed line control circuit individual to the local subscribers station shown in detail in Fig. 1. Threeother control circuits are shown inl diagrammatic form respectively` associated with the other subscribers stations shown in Figs. lhand2;

Figs. 5 and `6 show at the main switching office, key switching circuits respectively-connected to the control circuits of Fig. 4 and other keyswitch` ing circuits respectively connected to the` opera.- tors` teletypewriter sets. By `meansof these key switching circuits any line circuit `may be con-k nested to anyone of the operators teletype-writer sets or to one or more of the remaining.line` circuits;

Fig. '7v shows theoperators position and teletypewriter sets respectively connected to associated key switching circuits;

Fig.` 8 isthe cord switching `circuit which-inay` beyused as an alternative for the key switching` circuit shown in Figs. iand 6 l Fig.` 9 is arelative arrangement of` theiigures representingthe system when the key switchingA circuits are used; and

Figi. `l() is `arelative arrangement ofthe figures.

representingthe system wherein the cord switching circuits are used.

Referring.` to Fig. l, blocks Il, |02, |03, etc. represent station apparatus and, circuit, equipment for subscribers stations respectively connectedto the main station over local loop circuits and block H0 represents the stationapparatus and circuit equipment at one of several outlying subscribers stations located at considerably greater distances from the main office than the local subscribers stations. Each of thelocal sub` scribers stations and each of the `outlying stations are connected at the main station as shown,

that is, through a two-way halflduplex repeater and a control circuit, in series, to the operators switchboard. The outlying station is connected through a pair oi current reversing terminal lrepeaters in addition to the loop two-way half duplex repeater. The twofway half duplexlrepeaters used in the; local subscribersL loops are their A shown herein is: provided with nine local sub*- scribersstations lill, |92; |03, etc., and one or i thejoutlying subscribers stations I lil, nine looprepeater I3E|n of another type, and tencontrol alarm circuit |44 is adapted to be connected, in

common, directly to all the `control circuits.

DETAILED `Dcscnrerron `Assume that the line. circuit for SubscribcrsV station. No. 1sh`own. in the upper part of Fig. 2, is idle.v The line TR. is closed in a circuit traceable from a tap of a potentiometer comprising grounded positive battery 20|, resistances 2|9,

2I4, 213 and 2536, conductor 292, left-hand, orr

marking, contact and armature of polarized relay 283, conductor 294, `through the upper and lower windings, in parallel, of polarized relay 265, the path through the lower `winding extending through the artificial line 296 to ground, andlthe path through the upper winding extending through resistance 207, conductor T, through the winding of printermagnet 28, break key 209, transmitting contacts 2110, through the winding of.` receiving relay RR, normally closed contacts of five-second break key 2| conductor R.7 potentiometer P, resistance 2|2 to ground@ Relays 2533 and 205 are of the diiierential type and constitute the send relay and the receive relay respectively of repeater No. 1. The subscribers station shown somewhat in detail in Fig. 2 is of the well-known type which has ak normally closed line circuit somewhat of the type disclosed in United States Patent 2,114,023, granted to F. S. Kinkead on April l2, 1938, which shows a motor operating circuit of the remote control type. The receiv-` of a different type than those used inthe outlying subscribers station lines,` They will be `herein-` after described. There may bees many local subscribersi. stations-.andas cmany, outlying.V subing relay RR may be identied with its corresponding relay shown in the patent.

Local subscriber calls This will operate relay RR whereby a sequence of' operation takes place in a manner described in the patent and the subscribers teletypewriter motor starts operating when the key 209 is closed after the open interval of one second duration. The line circuit for subscribers station No. l includes, as hereinbefore stated, a repeateiI No. l designed to operate half duplex andrepeat telegraph signals in both directions between a volt,` 2Gmillia1npere current subscribers loop circuit and a 13G-volt inverse neutral, or hub, circuit. The only adjustment on the repeater is a potentiometer P of, say 3500 ohms, which is used for adjusting the loop current; -a receive relay 205 or" the polarized type is provided to receive i scr-ibers stationsas can besatisfactorilyoperatedl `in, an; intercommunicating system. The system the open interval of one-second duration, the repeater circuit of repeater No.1 is in the marking condition, as shown, due to a small current, say 20 milliamperes, flowing in the circuit hereinbefore traced through the upper winding of relay 205. Adjustments for this current may be made by means of potentiometer P in the circuit extending through the upper Winding of the relay, whereby the armature of relay 205 is normally held in its left-hand, or marking, position.

During the open interval of one second duration caused by break key 209 being operated, a spacing signal is transmitted from the loop and relay 205 is then operated to its spacing, or right-hand, position under the influence of the current 110W- ing through the lower Winding of the relay. When relay 205 operates to its spacing, or righthand, position, ground at the spacing contact is applied to the armature of relay 205, conductor 2|5, conductor 40|, through the Winding of line relay 402, to a tap on the potentiometer comprising resistance 403 and ground and resistance 404 and grounded battery 405. Relay 402 operates and disconnects at its armature and back contact ground connection 406 from condenser 401 and at its front contact connects ground connection 406 to 'the lament of vacuum tube 408 thereby causing the filament to light in a circuit traceable from grounded positive battery 409, resistance 4|0, conductors 4|| and 4|2, resistance 4|3, lament of tube 408, resistance 4|4, front contact and armature of relay 402, to ground connection 406. With ground connection 406 removed from condenser 401, grounded positive battery will now be permitted to ow through resistances 4 0, conduotors 4| and 4|2, resistance 415, conductor 4|0, condenser 401, resistance 4|1, to ground connection 418. When condenser 401 has assumed a sufficient positive charge, the grid of tube 408 will assume this positive potential and cause plate ourrent to flow through the Winding of plate relay |9. Relay 4|9 will, therefore, operate. Relay 4|9, upon operating, will connect ground over its armature and contact to a circuit which extends over the outermost right-hand armature and contact of relay 420, conductor 42|, inner armature and back contact of relay 422, conductor 423, through the filament of call lamp 50|, conductor 502, through the Winding of call relay 424, resistance M0, to grounded positive battery 409. Call lamp 50| will light and relay 424 will operate in series with the lamp. Relay 424, upon operating, locks up in a circuit traceable from grounded positive battery 409, resistance 4|0, through the Winding of relay 424, conductor 502, call lamp 50|,- conductor 423, contact and left-hand arma-ture of relay conductor 425, back Contact and inner right armature of relay 422, conductors 44| and 426 to ground at the back contact and innermost right-hand armature of broadcast relay 420. Relay 424, upon operating, also closes at its righthand armature and contact a circuit extending over conductor 421, release key 10|, audible alarm 102, source 103 of ringing current to ground. Audible alarm 102 operates to give the operator an audible signal in addition to the call signal oi lamp 50|. Audible alarm may be released by operating key 10|. Relay 424 Will remain in a locked position and call lamp 50| will be maintained lighted until the subscribers call has been answered by the operator.

Operator answers a call The operator answers the call by operating one of the keys 5| l, 5|2 and 5|3 to its upper orV lower .operators position set.

y of operating key 5|| Will also operate either key 503 or 506 to its upper position in order to connect one or the other of the operators position circuits 104 and 105 to the calling line extended from subscribers station No. l. The operation of key 5|| to its upper position closes a circuit extending from grounded positive battery 409, conductor 4||-, through the Winding of relay 422, middle left armature and Contact of relay 420, conductor 428, upper inner left-hand conta/cts of key 5| conductor 5|4, through the winding of relay 429, to ground at the back contact and innermost right-hand armature of relay 420. Relays 422 and 429 operate in series.

Relay 429, upon operating, connects together conductors, 2|1 and 2|8 in order to out through the receiving element, or relay 205, of the repeater No. 1. It also connects conductor 2 5 from the receiving element of repeater No. 1 to the transmission lead which extends to the selected Assume that the operator has selected position set 104, relay 429, upon operating, extends conductors 2|5 and 430 over its front contacts and right-hand armature to a circuit traceable over conductor 43|, outermost left-hand armature and back contact of relay 420, conductor 432, upper right-hand contacts of operated switch 51|, conductor 5|5 of hub H1, upper right-hand contacts of key 503 in an oper- `ated position, conductor 5|6, through the lower YWinding of receive relay 106 to grounded positive battery 101,

Relay 422, upon operating, closes a circuit extending from grounded positive battery 409, resistance 4|0, conductors 4| and 4|2, resistance 4|5, conductor 4|6, condenser 433, outer right armature and contact of relay 422, conductor 434, resistance 435 to ground connection 4|8 thereby placing condenser 433 in parallel with condenser 401 in order to increase the charging time constant from one second to five seconds for supervisory purposes. Also relay 422, upon operating, opens at its back contact and inner right armature the locking circuit for relay 424 to extinguish call lamp 50| and prepares a locking path for the subsequent operation of disconnect relay 436. Relay 422, upon operating, also opens at its outer left armature and contact the operating circuit for relay 420 if the system is arranged for non-seizure broadcast operation. In the event that the system is arranged for seizure broadcast operation, the outer left armature and contact of relay 422 are omitted and conductor 431 as shown by the dash line 443 is furnished.

The operator by plugging cords 10B and 109 into jacks 1 |0 and 1| I, respectively, connects the teletypewriter set No. l to her position circuit 104. The system is now arranged for communication between the subscribers station No. 1 and the operator at position set 104. During the transmission of signals from the subscribers station to the switchboard operator, polarized relay 106 Will follow the operation of relay 205 and thereby repeat the transmitted signals to the printer magnet in teletypewriter set No. 1. Relay 402 will also follow the signals repeated by relay '205 but since open intervals of five seconds duration are now necessary to cause plate current to flow in tube 408, the operation of relay 402 serves no useful function at this time other than to maintain condensers 433 and 401 in a discharged state. f i

During the transmission of signals from the switchboard operator to the subscribers station, polarized relay 113 will follow the signals transmitted from transmitting contacts of the operators` teletypewriter set No. l and relay 1106 responds to the operation ofrelay "1 13 to give a local copy of the transmitted message. Relay '1 I3 also repeats the locally transmitted signalsover the communication circuit to the subscribers station No.1, the communication circuit being traceable, as hereinbefore described, over conductors 5&3, 515, 432, 431, 430, 215, armature and marking, or left-hand, contact of relay 205, conductors 218 and `21'1,.through the upper winding of send relay2li3 to grounded battery. Relay 203 will V`follow the signals transmitted from the operators teletypewriter set No. 1 and repeat them through the parallelwindings of differential relay 205.` The path for recording the transmitted signals includes the winding of `printer `magnet 208 atisubscribers station No. 1. Printer magnet 208, in

` responseV to the transmitted signals, causes the message incoming at subscribers station No. 1

` to be printed. Relay 402 responds to the signals incoming at subscribers station No. 1 but the operation of this relay, like` hereinbefore stated,

` `serves no useful function at thistirne.

Subscriber disconnects l A subscriber Adisconnects by operating" the five second break key 216 whichwhen operatedcom- Fig. 4 to normal. After the subscriber has transmitted the open signal of five seconds duration, the subscriber should stand by for anacknowledgment by the operator and then inform the operator that a disconnect is desired. The subscriber may thenr either turn oil the powerthrough his teletypewriter by the operation of an upper case character on his` teletypewriter or leave this function to the operator. The operator may dothis by a similar operation on her teletypewriter. The subscriber should under no circumstances send a disconnect signal and then turn oil?` thepower as the operator will immediately challenge the validity of the disconnect and hence automatically again start up the subscribers teletypewriter. A substantial line opening or a teletypewriter signal will perform this function.

Operator originates a call yAssume that operators position circuit 104 is selected for use and that tnfe connection desired is with subscribers station No. l, the operator,

interconnected at the inner upper left-hand` contacts of key 511 to close a circuit for operating ate to a spacing condition whereby ground is connected to conductor 215 to operate relay 4022.` In this case, however, dueto relay 422beingA operated, condenser 433 `will be connected in.` parallel with condenser 40T inlorderto increase the tim-v ing constant from one second to ve seconds. After an interval of approximately ve seconds, a, sufficient positive potential will be impressed upon theigri'dof tube 408 causing plate current to ow through plate relay 419 which will` operate. `Since relay 422 has previously been operated,` theoperation of., relay 410will connect a.

ground at its armature and contact tota circuit extending over the outermostl right-hand armature and contact of relay 420, conductor421, inner left armature andfront contact of relay 422, conductors 438 andf518, disconnect lamp 511, conductor 439, through the-winding of disconnect relay 436', conductor 41 1, resistance 4.10, to grounded i positive battery 409.y The closure of this circuit will light disconnect lamp5`1f1 and operate relay 436 in series with `the. lamp.' `Relay 436, upcnoperating, closes a locking circuitfor itself traceable from grounded positive battery v4110, resistance 410, conductor 41 1through its winding, conductor` 439, lamp: 51T, conductorsvr 5.1;8` and 438, contact and left-hand armature ofrelay 436, conductor 440, front contactand inner right-hand armature of relay 422,ccnductors 4,41 and428 tol ground at the back contact and innermost right-hand armatureof relay142il. `Also relay 436,

upon operating, closes, at its right-hand armature and contact, a circuit `extending over conductor 4'2'1 to the audible alarm '102 to operate linekey 511; Key 511, upon'being restored to normal, restores the line control circuit shown iri` 7.3

ying through its upper winding.

relays 422 and 420 in series. Conductors 211 and 210 from the loop` repeater will be cut through and conductor 215 will be connected t0 the communication conductor which extends over conductors 431 and 432 and the closed right-hand contacts of keys` 511 and 533 respectively. The operator is now directly connected to the subscriber at station 1. However, the subscribers teletypevfriter has not yet been started. Moinentary operation of break lacy` 112 by the operator which causes a spacing condition to be transmitted to the hub circuit H1 and thence to the subscribers teletypewriter at station No. 1, will start the motor of the subscribers teletypewriter as described in U. S. Patent 2,114,023, supra. The operator may now cause the message to be typed directly on the subscribers tcletypewriter or, as is Well known in the art, may attract the attention of the attendant at subscribers station No. i, by actuating a bell signal character on her teletypewriter in order to cause a:

atorsposition set 'ifi-fi will be maintained in a` marking position, as shown, by the` current flow- When transmission takes place on the hub circuit Hi, a spacing condition which consists of a direct ground, will be intermittently connected to the hub circuit which will cause line current to iloW through thelower winding of receive relay '135; this lineA current being sufficiently in'eXcess of the biasing current in the upper winding of relay '106` will causerelay '13@ to follow these spacing signals. vThe intermittent operation of relay 106 will actuate theprinter magnet 714 of the operators teletypewriter set No. i and the teletypewriter will record the communication. When the operator wishes to transmit to any subscriber connected to the hub, operation of the keyboard on.

her teletypewriter set No. 1 will cause the sending contacts of the teletypewriter to be intermittently opened which will cause send relay '113 to follow these signals, since with no currentcondition in the lower winding the biasing current in the upper winding will operate relay I I3 to its spacing or left-hand contact. Intermittent operation of relay II3 to its spacing contact will connect ground to the hub which will cause functioning as described for relay 106 to any receiving circuit connected to the hub.

A spacing signal transmitted from the inverse neutral leg, or hub circuit, to the subscribers loop, applies ground to a circuit extending over conductor 2|5, armature and marking, or lefthand, contact of relay 205, conductor 2I8, contact and left-hand armature of relay 429, conductor 2I'I, through the upper winding of relay 203 to grounded positive battery. The ground applied to the upper winding of relay 203 sets up a current that is greater than the current flowing through the lower winding of relay 203 and the relay operates to its spacing, or right-hand, position. Relay 203, upon operating to its right-hand position, changes the potential applied to the apex of the balanced subscribers loop from +130 volts to ground. Since the balanced, or lower, winding of relay 205 is connected to a potentiometer through which current iiows from grounded positive 13G-volt battery 20| over resistances 2I9, 2I4, 2I3, and 206 to ground connection 220 and the subscribers loop is terminated at ground connection 22|, the operation of relay 203 reduces the current flow in the loop and in upper winding of relay 205 to zero while the current in the lower winding of relay 205 is reversed so that relay 205 will not operate to spacing. Therefore, the signals repeated by relay 203 are recorded at the printer at subscribers station No. 1.

Broadcast connection Means are provided whereby the operator may transmit from either of the teletypewriter sets shown to various groups of subscribers without being interrupted by these subscribers. This socalled broadcasting may be done on either a selective or grouping basis.

Selective broadcast Assuming that the operator selects position set '|04 for selective broadcast, key 'II5 will be operated to its left-hand, or selective, position. Key 1 I5, upon being operated to its left-hand position will connect ground to conductor 'II6. Also assuming that hub circuit H1 is selected for the broadcast, key 503 will be operated to its upper position and therefore conductor TIG will be connected over the outermost upper left-hand contacts of key 593 to conductor 5I8 of hub circuit H1. Assume that lines No. I, No. 2 and No. 3 are to be included in the broadcast, keys 5I I, 50| and 6I| will be operated to their respective upper positions. The ground connection on conductor IIS will therefore be connected at each of switches 5I I, 09| and GII to each of two conductors extending to each of the subscribers stations included in the broadcast. The conductors extending to the subscriber at station No. to which this ground is connected are designated 428 and 5|4. Conductor 428 extends over the l middle left-hand armature and contact of broadcast relay 420, through the winding of relay 422 to grounded positive battery 409 and relay 422 operates. However the ground connected to con- F condition between conductor 2|5 and the communication conductors 43| and 432 which eX- tends over conductor 5|5 of the hub circuit H1. Also relay 429, being in a. released position, prevents conductor 2H from being connected to Conductor 240 and maintains conductor 2 I'I'connected transmission conductors 43| and 432. The operator may thus transmit to the subscriber over conductor 2II to the loop repeater. At the same time the operator may receive supervision from the subscriber at station No. I over conductor ZIE. This is important when a group of lines are connected for a broadcast. In the case of the broadcast to subscriber stations No. 2 and No. 3 the function performed and the results obtained are the same as those described herein for subscriber station No. I.

Group broadcast For group broadcast the operator may broadcast to any selected group of lines. These lines are arranged beforehand to provide for this service. The operator operates broadcast key 1 I5 to its right-hand, or group, position and ground is thereby connected to the winding of relay '|26 in an obvious operating circuit. Relay '|25` operates to connect at its innermost upper armature and contact a ground connection to conductor IIIi to perform denite functions as hereinbefore described for selective broadcast. At the middle upper armature of relay '|26 ground is connected to conductors 1II and 448 in a circuit extending through the winding of broadcast relay 420, conductor 442, conductor 443 (providing the line circuit is arranged on a seizure basis), conductors 431 and 4| I, resistance 4|0, grounded positive battery 409. As hereinbefore stated for selective broadcast operation, relay 429 remains in a released position and relay 422 operates. In this case conductor 2I1 from the loop repeater is connected directly to the operators position circuit '|04 over the outermost left armature and front contact of relay 420,'broadcast communication conductor 444, outermost upper armature and contact of relay H3, conductor 5I6 to grounded positive battery either through the lower winding of relay '|00 or the armature and marking contact ofl relay 'II3, depending upon whether the communication is being received or transmitted at the operators position circuit |04. Should the line circuit be not arranged on a seizure basis conductor 443 would be omitted and the operation of broadcast relay 420 would depend on whether this line circuit is in a busy condition. If this line circuit is busy relay 422 will be operated andl hence the operating path for relay 420 will be opened and thus prevent broadcast to this line even though it is arranged for group broadcast. As hereinbefore stated, for selective broadcast the operator only can transmit communication signals. The subnals to the operator.

Outlying subscriber calls In cases where the distance between the main station and an outlying subscriber station is in excess of thirty-eight miles a special type of repeater indicated in Fig. 3 as repeater No. I0 is required. Station No. 10 shown in Fig. 3 represents an outlying station connected through a current reversal terminal repeater of a type well known in the art and shown in U. S. Patent 1,935,750 granted to F. J. Singer on November 21, 1933.

The subscriber line circuit is of the same type as that shown for station No. 1 but extends through a differential duplex two-path polar telegraph terminal repeater, as shown, whereof relays 301, 302' and 303 are the send, the receive and the break relayson the station side of the repeater and relays 304, 305and 306 are the send, the receive and the break relays on the line side `of the repeater. The line then extends through a second repeater of the single line type whereof one side operates open and closed to a neutral loop. This operation is accomplished by having the receive relay 301 which receives from the neutral loop and sends into the inverse neutral loop, equipped with a combination bias and holding circuit. The other side of this, repeater is arranged for operating into an inverse neutral circuit referred to herein as a hub circuit.

Normal conlclz'tionof loop repeater In thenormal condition of this repeater when no signals are being transmitted in either direction, current is flowing in the loop circuit which extends back through the terminal repeater to the subscriber station.' Relay 301 of the loop repeater and relay 301 to relay 306 of the terminal repeater are thereby held in the positions shown. Under these conditions no current flows in the line side of the loop repeater. Send relay 303 and hold relay 309` are maintained in the positions shown by current of approximately 16 milliamperes flowing through their respective lower windings. The loop or station side of the repeater isclosed through the armature and marking, or left-hand, contact of send relay 308. Current flows from grounded positive battery 310 in a circuit traceable through resistances 31 I and 312, tap 313 of the potentiometer, through the lower winding" of relay 301, resistance 314, retardation coil 315, marking, or left-hand, contact and armature of relay 309 to ground. This current tends to operate relay 301 to its spacing, or left-hand contact, but since it is one-half the magnitude of the currentin the loop, relay 301 is held in itsmarking, or right-hand,.posi tion.

Transmission of signals from inverse neutral circuit to neutral loop A spacing signal from the inverse neutral ciri cuit which is transmitted to the repeater by ap-` plying ground to conductor 311i` causes a currentl of approximately 20 milliamperes to flow through the upper windings of relays 308 and` 3,09. Under this condition a current of approximately 4 milliamperes flows in the lower windings of these` relays. Since the current` in the upper windings is oppositely poledand 16 milliamperes greater than the current flowing in the lower windings, relays 308 and 309 operate to their spacing, or righthand, contacts. will transmit unbiased signals to the neutral loop since the difference in the current in the upper and the lower windings is the same for both the marking and spacing conditions, namely, 16 milliamperes. ing of relay309 is shunted by resistance 311, the current flowing in this winding is less than the current flowing through the lower winding of relay 308. Therefore, relay 309 operates to spacing, that is, its right-hand contact before relay 309. Relay 309, upon operating to spacing, causes current in the lower winding of relay 301 to reverse and hold relay 301 in itsmarking, or right- It will be Iseen that relay 308` Due to the fact that the lower wind-- hand; position.- The reversal of current through relay 301 is` accomplished by means of the resistance bridge consisting of resistance 311 as one arm, resistance 312 as the second arm, resistance 318 as the third arm and resistance 314, retard coil 315, left-hand contact and armature of relay 309 to ground as the fourth arm. The lower winding of -relay 301 is connected across the bridge points. The resistances are so arranged that when relay 301 is in the position shown, current will iiow from-grounded positive battery 3'0, through the lower winding of relay 30.1 inasmuch as the resistance of path including resistance 314 and retard coil 315 is less than the resistance and the path including resistance 311. Resistances 312 and 318 have approximately the same values.

When relay 300 operates to its spacing, or righthand, position, current will iiow through the lower winding. of relay 301 in the` opposite direction inasmuch as the path including resistance 314 .and retard coil 315 is open. Therefore, before relay 308 operates to its spacing, or righthand, position and opens the loop circuit, relay 301 will be held on its marking, or right-hand,

position.

A marking signal from the inverse neutral circuit which is transmitted to the repeater by removing ground from conductor 316 causes relays 308.` and 39to operate to their marking, or lefthand, position. However, relay 308 operates before relay 309 since the current owing in the lower winding of relay 308 is greater than that flowing-in the lower winding of relay 300. Relay l 308 thus closes the loop circuitextending. throughthe upper winding of relay 3371 before relay 309 has operated to marking. When relay 309 operates to marking it closes one arm of the` bridge circuit previously described and the resultant curi rent owing in the lower winding of relay 301.

tends to operate relay 301 to spacing, but since this current is one-half the magnitude of the current.. in the loop circuit relay 301 is held in its marking position. In order tofurther delay the,

i reversal current in the lower windingf of relay 30.1

the retard coil 315 is used to retard the rise in current to` this winding afterV the armature of relay 309 has moved into engagement with its` left-hand, or marking, Contact.

' Transrm'ssiony of signal from neatra'lto inverse neutral Zoop A spacing signal transmitted from the neutral loop reduces the loop current to zero and the current flowing through the lower winding of relay 301 operates the relay into spacing. Relay 301, upon moving to its spacing position, applies ground to conductor 310 and thus transmits a spacing` signal to the inverse neutral circuit. A marking signal transmitted from the neutral loop reestablishes the loop circuit and operates relay 301v to `its marking position. Relay 301, upon operating toitsmarking position, applies battery to conductor 311i and thus transmits a marking `.signal to vthe `inverse neutral circuit.

capable of associating line No. I with any one of the hub circuits H1 to H6. A description of a connection originating at station No. I0 or at either of the operators teletypewriter sets Nos. I and 2, shown in Fig. '7 for extension to stations No. I0 or to two or more of the other stations for broadcast purposes may be established in a mannersimilar to that hereinbefore described in connection with station No. I.

Cord switching circuits In the event that it is desired to use cord switching circuits instead of the key switching circuits shown in Figs. and 6, cord switching circuits such as those designated Nos. I and 2 in Fig. 8 are adapted to serve substantially the same purpose as the key switching circuits. Each of the line circuits connecting the subscriber stations with the main station terminate at an operators switchboard in the main station as represented by conductor group 80! for line circuit No. I. Assuming that a call originates at subscriber station No. I, a light will appear at call lamp 802 in the same manner as a call appears on lamp 50| as hereinbefore described. The operator at either of the teletypewriter sets Nos. I and 2, upon observing the lighted lamp inserts the answering plug 803 of the cord circuit associated with the selected teletypewriter set, say set No. I, into jack 804. Assuming that teletypewriter set No. I is selected for use and answering plug 803 is inserted in jack 804 then the operators position key 805 is operated to its lower position in order that teletypewriter set No. I may be connected to line No. I. A circuit is now closed from grounded positive battery 101 through the lower winding of polarized relay '106, conductors 5I6 and 806, lower right Contact of key 805, conductor 801, ring conductors of plug 803 and jack 804, conductors 432 and 43|. Plug 803, upon being inserted in jack 804, also closes contact 808 whereby conductors 428 and 5I4 are interconnected to effect the operation of relays 429 and 422 and to thereby cause the extinguishment of call lamp 802. Communication may now take place between the operator and subscriber at station No. I. The operator upon receiving the information regarding the called subscribers station may then complete the connection by inserting the call, or opposite, end of cord circuit No. I into the line jack of the called line.

Operator originates the call The operator originates the call by inserting the call end of a cord circuit, for example, cord vcircuit No. I into a line jack of the called line and Disconnect from subscriber stations When a subscriber disconnects, the operation of the control circuit is the same as hereinbefore described and the disconnect lamp 809 is lighted.

` The operator then disconnects by removing the answer and call plugs from the line jacks and restoring the teletypewriter key to normal.

Broadcast The operator may arrange any line for broadcast transmission. After the connection has been established as hereinbeiore described and the operator is connected to the subscribers station, the operator will operate a broadcast key in the operators position circuit. The operation of a broadcast key, such as key l' I5, to its left-hand position, connects ground to conductor 'I I6, lower left-hand contacts of key 805, conductor 8I0. sleeve conductors of cord circuit No` I and jack 808, conductor 554, through the winding of relay 429 to ground at the back contact and innermost right-hand armature of relay 420. Relay 429 having ground at opposite ends of its operating circiut does not operate as hereinbefore described under broadcast conditions. However, the ground connected at key 'I i5 is also connected to conductor 428 which is part of a path extending over the contact and middle left armature of relay 420, through the winding of relay 422', to grounded positive battery 409. With relay 422 operated and relay 429 maintained in a released position, the control circuit operates the same as hereinbefore described.. The operator has arranged a line circuit for broadcast with provision being made for supervisory control from the subscriber. In the case of the operator having more than one line circuit arranged for broadcast on the same hub circuit, this individual supervisory control from each subscriber is important as otherwise the operator would not know which subscriber was sending disconnect signals which might be used for broadcast acknowledgment. Since there are two operators teletypewriter sets available, two broadcast circuits may be established, one by each operator. Each operator may add lilies to a broadcast group by inserting the plugs of other cord circuits into those line circuits and operating the teletypewriter key of each cord circuit to the teletypewriter set used in the broadcast.

Conference The operator may arrange any group of lines for conference with each other. Two separate conference circuits are possible, one branch using one hub grouping and the other branch using the other hub grouping. When a conference connection is requested by a subscriber, the operator will connect the plugs of the cord circuits to the line circuit involved and operate the grouping key for each cord circuit to the same grouping position. For example, grouping key 8I0 may be operated to either its upper or lower positions. This will connect all these lines to the same hub circuit for hub operation. A second conference circuit would be established in the same manner except that the grouping key for the second group of cord circuits would be operated to the other grouping position thus connecting this group of lines to the other hub for hub operation.

Alarm circuit Two types of alarm circuit are furnished. One alarm circuit is of the audible type wherein a buzzer, bell or other audible device like that designated '102 may be employed and key IUI is furnished for shutting off the alarm. Another alarm circuit is that for giving or furnishing a signal whenever a fuse in the fuse panel burns out in which event grounded battery 'H8 and alarm relay 'I I9 are interconnected through the burntout fuse whereby the relay operates to light signal lamp and to energize audible signal 102.

By operating key 12|, lamp 120 may be extinguished and audible alarm 102 may be disconnected. m

What is claimed is:

1. A switching system comprising a plurality of line circuits and individual signaling sets therefor, plurality of control circuits in engageablerelation with said plurality ofline circuits respectively, a group of switching devices for each or said Vcontrol circuits, a plurality of hub circuits, each of which is in engageable relation with the switching devices of different groups, other groups of switching devices and operators signaling sets respectively connected thereto, and means operable in response to the conjoint operation of one or more of said switching devices of the first-mentioned group and one or more of the switching devices of said other groups to simultaneously interconnect over one or more of said hub circuits one or more of said individual signaling sets and one or more of said operators signaling sets.

3. A switching system comprising a plurality` of circuits and individual signaling sets therefor, a group of switching devices for each of ysaid circuits, a plurality of hub circuits, each arranged in engageable relation with the switching devices of dilerent groups, other groups of switching devices in engageable relation with said hub circuits, operators signaling sets respectively connected to said other groups, and means `common to said `hub circuits and operable in one direction for selectively connecting, in conjunction with the operation of two or more switching devices in engageable relation with any one of said hub circuits, two or more of said individual signaling sets, in multiple, to any one of said operators signaling sets 'for intersignaling purposes, and operable in another `direction for connecting, independent of said switching devices, two of more of said individual signaling sets, in multiple, to any one of `said operators signaling sets for intersignaling purposes.

4. A switching system comprising a plurality of lines and control circuits individual thereto, a plurality of operators position sets, a plurality of switching device groups respectively terminating said control circuits, a plurality of other switching device groupsl respectively terminating said operators position sets, a plurality of hub circuits in engageable relation with corresponding switching devices of each of said plurality of groups, means controlled by said switching devices for preparing a connection between any one of said lines, and one or more of theremaining of said lines, and means in each of said control circuits controlled by any one of said switching devices terminating its particular control circuit, for transferring the line circuit associated with said particular control circuit from an established signaling connection to a communication connection.

5. A switching system according to claim 4 wherein said switching devices are manually` operable keys.

6. A switching system according to claim 4 wherein said switching devices are cord circuits and spring jacks therefor and manually operable keys cooperating with each of said cord circuits.

7. A printing telegraph system comprising a plurality of telegraph lines and control circuits respectively connected thereto, a plurality of operators position sets, a plurality of switching devices respectively terminating said control circuits, a plurality of other switching devices for'respectively terminating said operators position sets, a plurality of hub circuits, each common to separate terminations of said control circuits and said operators position sets, means operable in response to the conjoint operation of one or more of said switching devices of the first-mentioned group and one or more of the switching devices of said other groups to simultaneously interconnect over one or more of said hub circuits one or more of said lines and one` or more of said operators position sets, and other means in each of said operators position sets operable, in one direction, conjointly with each of the switching devices terminating its associated operators position set and with a terminating switching device of each of said control circuits, to selectively establish a communication connection between said one operators position set and two or` more of said lines over one of said hub circuits, and operable in the other direction and independently of said switching devices and said hub circuit to establish a direct communication circuit between said one operators position set and the control circuits of a fixed group of two or more of said lines.

8. A printing telegraph system comprising a plurality of telegraph lines each including, in series connection, a repeater circuit and a control circuit, a plurality of operators position sets and one or more of the switching devices of said other.

groups to simultaneously interconnect over one or more of said hub circuits one or more `of said lines and one-or more of said operators position sets, and other means controlled .by said repeater and said control circuit for permitting supervisory signals ,'to be transmitted to an operators position set during an established connection between two or more of said lines and an operators position set.

FULLERTON S. KINKEAD. JOSEPH A. KRECEK. 

